1. Field of the Invention
The present invention relates to a communication node for carrying out data transfer between a first network and a second network, and a communication terminal for carrying out communications with a node on a second network by being connected to a first network.
2. Description of the Background Art
In recent years, the home network formation has been attracting much attention, but such a concept itself is not new and, in particular, the standard specifications such as CEBus and LON have already been proposed for the home network aiming at the home security. In addition, the analog AV cables (white, red, and yellow cables) for connecting AV (Audio Visual) devices can also be regarded as a kind of home network. As such, there have been potential demands for the home network formation even conventionally, but currently it has not come to be used widely except for the AV cables for connecting AV devices, and it can be said that the home network formation has hardly progressed yet.
This is due to problems including that the connections with the other home networks or PCs cannot be made because the conventional AV cables carries out the data transfer using analog signals, and that the conventional home network such as CEBus and LON can only transfer narrow bandwidth data. In addition, the fact that users could not have enjoyed many merits from the conventional home network formation appears to be the major obstacle for its spread.
In view of these problems, a new standard for serial bus called IEEE 1394 that has been developed as a next generation version of SCSI is attracting much attention in recent years. The IEEE 1394 bus is designed such that a plurality of terminals can be connected either in a daisy chain or in a star connection, and wide bandwidth data of over 100 Mbps can be transferred. Also, its most characteristic feature is the fact that both Asynchronous data and Isochronous data can be transmitted on the same cable. For this reason, there are increasingly active trends for using the IEEE 1394 as a cable for connecting AV devices despite of the fact that the IEEE 1394 was originally developed as a next generation version of SCSI.
With this technique, large capacity data such as image information to be transferred between AV devices that have conventionally been transferred by the analog transmission can now be transferred by digital signals using the Isochronous data transfer function of the IEEE 1394. For this reason, in addition to the existing function for connecting AV devices, there is also a function for connecting AV devices with digital devices such as PC so that this technique is attracting much attention lately. In addition, in recent years, there are several propositions for a way of realizing this IEEE 1394 bus even in the radio environment. For instance, an attempt for transferring 100 Mbps of data using the infrared rays and an attempt for implementing the IEEE 1394 protocol on the wide bandwidth radio using high frequency band are have been initiated.
Also, as a way of realizing the radio network in home, a new home radio network has been discussed by an organization called HRFWG (Home Radio Frequency Working Group) which is centered around the Microsoft Inc. of U.S.A. These radio networks basically realize the data transfer between a radio terminal and a node having a base station function on the IEEE 1394 bus, and it is expected that the interworking function with respect to the IEEE 1394 bus will become an indispensable function.
In order to realize such an interworking processing with respect to the IEEE 1394, several functions become necessary. For example, in the case of transferring some kind of compressed image data from a node on the IEEE 1394 bus toward a radio terminal, it is impossible to ascertain what kind of image information should be transferred unless it is possible to ascertain a kind of image data decoding function provided at the radio terminal and a king of image information (how it is encoded, etc.) possessed by the node on the IEEE 1394 bus.
Thus there are increasingly active trends for using the IEEE 1394 as a cable for connecting AV devices, and there are several propositions for realizing the IEEE 1394 bus even in the radio environment. However, the proposition such as the infrared 1394 basically contemplates the direct application of the IEEE 1394 protocol to the radio section, and it has been pointed out that such a proposition does not match the actual IEEE 1394 bus utilization states. In particular, it is expected that the route blocking in the radio section will directly influences the bus reset function of the IEEE 1394 bus, so that there will be a problem that communications on the IEEE 1394 bus will be frequently interrupted due to the route blocking in the radio section.